
The following examples show how to find a mover's position at a certain time or for a certain time span.
import pandas as pd
import geopandas as gpd
import movingpandas as mpd
import shapely as shp
import hvplot.pandas
from geopandas import GeoDataFrame, read_file
from shapely.geometry import Point, LineString, Polygon
from datetime import datetime, timedelta
from holoviews import opts
import warnings
warnings.filterwarnings('ignore')
opts.defaults(opts.Overlay(active_tools=['wheel_zoom'], frame_width=500, frame_height=400))
mpd.show_versions()
MovingPandas 0.10.rc1 SYSTEM INFO ----------- python : 3.9.13 | packaged by conda-forge | (main, May 27 2022, 16:50:36) [MSC v.1929 64 bit (AMD64)] executable : H:\miniconda3\envs\mpd-ex\python.exe machine : Windows-10-10.0.19043-SP0 GEOS, GDAL, PROJ INFO --------------------- GEOS : None GEOS lib : None GDAL : 3.5.0 GDAL data dir: None PROJ : 9.0.0 PROJ data dir: H:\miniconda3\pkgs\proj-9.0.0-h1cfcee9_1\Library\share\proj PYTHON DEPENDENCIES ------------------- geopandas : 0.10.2 pandas : 1.4.2 fiona : 1.8.21 numpy : 1.22.4 shapely : 1.8.2 rtree : 1.0.0 pyproj : 3.3.1 matplotlib : 3.5.2 mapclassify: 2.4.3 geopy : 2.2.0 holoviews : 1.14.9 hvplot : 0.8.0 geoviews : 1.9.5 stonesoup : 0.1b9
First, let's create a basic trajectory:
df = pd.DataFrame([
{'geometry':Point(0,0), 't':datetime(2018,1,1,12,0,0)},
{'geometry':Point(6,0), 't':datetime(2018,1,1,12,6,0)},
{'geometry':Point(6,6), 't':datetime(2018,1,1,12,10,0)},
{'geometry':Point(9,9), 't':datetime(2018,1,1,12,15,0)}
]).set_index('t')
gdf = GeoDataFrame(df, crs=31256)
toy_traj = mpd.Trajectory(gdf, 1)
toy_traj
Trajectory 1 (2018-01-01 12:00:00 to 2018-01-01 12:15:00) | Size: 4 | Length: 16.2m Bounds: (0.0, 0.0, 9.0, 9.0) LINESTRING (0 0, 6 0, 6 6, 9 9)
help(mpd.Trajectory.get_position_at)
Help on function get_position_at in module movingpandas.trajectory:
get_position_at(self, t, method='interpolated')
Compute and return position at time t.
Parameters
----------
t : datetime.datetime
Timestamp to extract a row for
method : str
Interpolation method
Returns
-------
shapely Point
Position at time t
Examples
--------
If the trajectory contains a position at the given timestamp, it is
returned:
>>> traj.get_position_at(datetime(2018, 1, 1, 12, 6))
Point (6 0)
If there is no trajectory position for the given timestamp, the default
behaviour is to interpolate the location:
>>> traj.get_position_at(datetime(2018, 1, 1, 12, 9))
POINT (6 4.5)
To get the trajectory position closest to the given timestamp, specify
method='nearest':
>>> traj.get_position_at(datetime(2018, 1, 1, 12, 9), method='nearest')
POINT (6 6)
When we call this method, the resulting point is directly rendered:
toy_traj.get_position_at(datetime(2018,1,1,12,6,0), method="nearest")
To see its coordinates, we can look at the print output:
print(toy_traj.get_position_at(datetime(2018,1,1,12,6,0), method="nearest"))
POINT (6 0)
The method parameter describes what the function should do if there is no entry in the trajectory GeoDataFrame for the specified timestamp.
For example, there is no entry at 2018-01-01 12:07:00
toy_traj.df
| geometry | |
|---|---|
| t | |
| 2018-01-01 12:00:00 | POINT (0.000 0.000) |
| 2018-01-01 12:06:00 | POINT (6.000 0.000) |
| 2018-01-01 12:10:00 | POINT (6.000 6.000) |
| 2018-01-01 12:15:00 | POINT (9.000 9.000) |
t = datetime(2018,1,1,12,7,0)
print(toy_traj.get_position_at(t, method="nearest"))
print(toy_traj.get_position_at(t, method="interpolated"))
print(toy_traj.get_position_at(t, method="ffill")) # from the previous row
print(toy_traj.get_position_at(t, method="bfill")) # from the following row
POINT (6 0) POINT (6 1.5) POINT (6 0) POINT (6 6)
point = toy_traj.get_position_at(t, method="interpolated")
df = pd.DataFrame([{'id': toy_traj.id, 'geometry': point, 't': t}])
gdf = GeoDataFrame(df, crs=toy_traj.crs)
ax = toy_traj.plot()
gdf.plot(ax=ax, color='red', markersize=100)
<AxesSubplot:>
First, let's extract the trajectory segment for a certain time period:
help(mpd.Trajectory.get_segment_between)
Help on function get_segment_between in module movingpandas.trajectory:
get_segment_between(self, t1, t2)
Return Trajectory segment between times t1 and t2.
Parameters
----------
t1 : datetime.datetime
Start time for the segment
t2 : datetime.datetime
End time for the segment
Returns
-------
Trajectory
Extracted trajectory segment
segment = toy_traj.get_segment_between(datetime(2018,1,1,12,6,0), datetime(2018,1,1,12,12,0))
print(segment)
Trajectory 1_2018-01-01 12:06:00 (2018-01-01 12:06:00 to 2018-01-01 12:10:00) | Size: 2 | Length: 6.0m Bounds: (6.0, 0.0, 6.0, 6.0) LINESTRING (6 0, 6 6)
ax = toy_traj.plot()
segment.plot(ax=ax, color='red', linewidth=5)
<AxesSubplot:>
Now, let's extract the trajectory segment that intersects with a given polygon:
xmin, xmax, ymin, ymax = 2, 8, -10, 5
polygon = Polygon([(xmin, ymin), (xmin, ymax), (xmax, ymax), (xmax, ymin), (xmin, ymin)])
polygon
polygon_gdf = GeoDataFrame(pd.DataFrame([{'geometry':polygon, 'id':1}]), crs=31256)
help(mpd.Trajectory.clip)
Help on function clip in module movingpandas.trajectory:
clip(self, polygon, point_based=False)
Return trajectory segments clipped by the given polygon.
By default, the trajectory's line representation is clipped by the
polygon. If pointbased=True, the trajectory's point representation is
used instead, leading to shorter segments.
Parameters
----------
polygon : shapely Polygon
Polygon to clip with
point_based : bool
Clipping method
Returns
-------
TrajectoryCollection
Clipped trajectory segments
intersections = toy_traj.clip(polygon)
intersections
TrajectoryCollection with 1 trajectories
ax = toy_traj.plot()
polygon_gdf.plot(ax=ax, color='lightgray')
intersections.plot(ax=ax, color='red', linewidth=5, capstyle='round')
<AxesSubplot:>